Signal Conversion Efficiency Research Articles

Tuning the conversion efficiency of high-order harmonic signals via variation of the Porras factor

Tuning the conversion efficiency of high-order harmonic signals via variation of the Porras factor

Broadband infrared imaging governed by guided-mode resonance in dielectric metasurfaces

Nonlinear metasurfaces have experienced rapid growth recently due to their potential in various applications, including infrared imaging and spectroscopy. However, due to the low conversion efficiencies of metasurfaces, several strategies have been adopted to enhance their performances, including employing resonances at signal or nonlinear emission wavelengths. This strategy results in a narrow operational band of the nonlinear metasurfaces, which has bottlenecked many applications, including nonlinear holography, image encoding, and nonlinear metalenses. Here, we overcome this issue by introducing a new nonlinear imaging platform utilizing a pump beam to enhance signal conversion through four-wave mixing (FWM), whereby the metasurface is resonant at the pump wavelength rather than the signal or nonlinear emissions. As a result, we demonstrate broadband nonlinear imaging for arbitrary objects using metasurfaces. A silicon disk-on-slab metasurface is introduced with an excitable guided-mode resonance at the pump wavelength. This enabled direct conversion of a broad IR image ranging from >1000 to 4000 nm into visible. Importantly, adopting FWM substantially reduces the dependence on high-power signal inputs or resonant features at the signal beam of nonlinear imaging by utilizing the quadratic relationship between the pump beam intensity and the signal conversion efficiency. Our results, therefore, unlock the potential for broadband infrared imaging capabilities with metasurfaces, making a promising advancement for next-generation all-optical infrared imaging techniques with chip-scale photonic devices.

Clinically applicable assay of cardiac troponin I by CRISPR/Cas12a-amplified single-particle collision electrochemistry

Owing to its rapid response and ultra-high sensitivity at single-entity level, single-particle collision electrochemistry (SPCE) shows great application prospects in sensitive detection of biomolecules. However, its widespread use in actual samples is constrained by the poor signal conversion efficiency and heavy interference from complicated samples. Here, a new SPCE biosensor for clinical analysis of cardiac troponin I (cTnI) was developed based on the effective signal amplification of CRISPR/Cas12a as well as the good separation and enrichment capabilities of magnetic nanobeads (MBs). The trans-cleavage capability of CRISPR/Cas12a can only be triggered in the presence of target cTnI to effectively cleave ssDNA2 on the surface of Au@Pt nanoparticles (Au@Pt NPs) within 30 min. Each cTnI molecule could cause the release of 4.68×104 Au@Pt NPs by utilizing the superior cleaving activity of CRISPR/Cas12a, significantly amplifying the signal and improving the sensitivity of analysis. The developed SPCE biosensor for cTnI had a detection limit as low as 0.35 fg/mL, which was 2–6 orders in magnitude less than existing cTnI detection techniques. Additionally, MBs allow the biosensor to detect cTnI in patient samples with excellent sensitivity and specificity by directly sampling from the complex matrix.

Measurement of nonlinear three-wave interaction using shear-vertical-wave point-focusing electromagnetic acoustic transducers

Abstract We developed a method of nonlinear three-wave interaction using shear-vertical-wave point-focusing electromagnetic acoustic transducers (SV-wave PF-EMATs). EMATs can excite and detect ultrasonic waves without couplants through interaction between electromagnetic fields and solid mechanics and are generally unsuitable for the nonlinear ultrasound measurement due to their low signal conversion efficiency. However, our originally developed PF-EMAT can focus SV waves at a focal point in phase, achieving a large local displacement. Here, two PF-EMATs with different driving frequencies are placed facing each other so as to match their focal points, where the focused SV waves intersect to induce the third waves with the frequencies of the sum and difference of the incident frequencies through the nonlinear three-wave interaction. We demonstrate that the local nonlinearity can be measured by this method with EMATs and demonstrate its applicability to evaluation of fatigue damage in a fatigue crack initiation phase with aluminum alloy specimens.

Enhancing conversion efficiency of MgO:PPLN and Rb:PPKTP crystal-based subnanosecond optical parametric generators by utilizing a supercontinuum seed

This paper presents an approach to enhance the conversion efficiency of subnanosecond pulse duration microlaser-pumped optical parametric generators (OPGs) tunable from near- to mid-infrared. The method involves generating a supercontinuum (SC) in the photonic crystal fiber (PCF) and using it to seed the subnanosecond OPG based on the fan-out grating design MgO:PPLN crystal. Since the SC spectrum covered the entire signal wave tuning range (1414–2128 nm), seeding and conversion efficiency improvement of 6%–11% was achieved for all OPG signal wavelengths, and the generation threshold was reduced up to 3 times. Such a method allows for improved energy stability, significantly increases the brightness of the OPG output radiation, and is pivotal in mitigating the risk of MgO:PPLN optical damage. The study also extended the method to successfully seed 532 nm pumped Rb-doped PPKTP crystal-based OPG with the same SC, demonstrating broad applicability and performance improvement across different parametric devices.

Influence of diamond matrix morphology on ZnO surface morphology and preferred orientation

The signal propagation loss and conversion efficiency are two critical performances of diamond/ZnO film-based surface acoustic wave (SAW) device, and depend on roughness and preferred orientation degree (POD) of ZnO surface layer at plane (002). In-situ improvement of operational performance of ZnO layer is achieved by adjusting morphology of diamond matrix layer via diamond particle size. Diamond layer is deposited on silicon substrate using hot-filament chemical vapor deposition (HFCVD) technique by varying Ar/(Ar+H2) ratio. The ZnO layer is then deposited on the diamond film using radio-frequency magnetron sputtering (RFMS). The results show that, by regulating the diamond particle size, it is possible to adjust morphology of the diamond layer and facilitate variation in morphology and preferred orientation of ZnO layer for a better operational performance of SAW device. When the diamond particle size is decreased from 1.38 to 0.12 µm, the root-mean-square (RMS) roughness of ZnO layer initially drops and then rises, and the lowest roughness is 6.4 nm. Also, POD of ZnO (002) increases from 2.61 to 2.89, and then drops to 2.83. For a diamond particle size of 0.35 µm, the RMS roughness of ZnO layer has minimum value of 6.4 nm, and the POD of ZnO (002) approaches the maximum of 2.89 with a half-peak width of 0.36˚. The influence of diamond layer morphology on ZnO morphology and POD is thus proposed.

Non-destructive periodic poling quality evaluation of MgO:PPLN and Rb:PPKTP crystals based on crystal translation and parametric light generation

The work discloses a flexible, non-destructive, aberration-free, and automated periodic poling quality evaluation technique of the periodically poled crystals in the whole volume of the crystal with very high control and resolution. The method is based on a crystal translation in the directions perpendicular to the pump laser beam and the simultaneous recording of the parametric signal conversion efficiency in a simple single-pass parametric light generator setup. This technique allowed us to investigate and quantitatively describe the ferroelectric domain structure homogeneity of the periodically poled lithium niobate and potassium titanyl phosphate crystals with single, multi, and fan-out grating designs and offers a practicable overall efficiency assessment of the quasi-phase-matched device.

Temporal Contrast Enhancement Based on the Self-Diffraction Process with Different Kerr Media

In this study, the self-diffraction (SD) process proved to be a competitive method to achieve a seed pulse with high temporal contrast in ultra-intense lasers. Several different nonlinear, transparent Kerr media including BK7 glasses, AL2O3 and CVD diamonds were compared experimentally to obtain SD signals with high energy and high conversion efficiency. AL2O3, with a high third-order nonlinear coefficient and high laser damage threshold, was found to be the best medium to improve the conversion efficiency of SD signals. The highest first-order SD signal of 401.7 μJ was achieved, with the conversion efficiency at approximately 9.1%, when the incident pulse energy was 4.40 mJ. The temporal contrast of the obtained first-order SD signal was improved by 7 orders of magnitude to 1012. As a result, this cleaning pulse will facilitate research involving ultra-intense laser systems and high-intensity laser–matter interactions.

Magnetic Rolling Circle Amplification-Assisted Single-Particle Collision Immunosensor for Ultrasensitive Detection of Cardiac Troponin I.

Owing to its simplicity, high throughput, and ultrasensitivity, single-particle collision electrochemistry (SPCE) has attracted great attention in biosensing, especially labeled SPCE. However, the low signal conversion efficiency and much interference from complex samples limit its wide application. Here, a new and robust SPCE immunosensor was proposed for ultrasensitive cardiac troponin I (cTnI) detection by combining target-driven rolling circle amplification (RCA) with magnetic beads (MBs). Antibody-modified MBs have good stability, dispersity, and magnetic response capacity in complex samples, enabling efficient capture and separation of cTnI with high specificity and anti-interference ability. The presence of cTnI could specifically drive the formation of magnetic immunocomplexes followed by triggering RCA and enzyme digestion reaction. By using Pt nanoparticles (Pt NPs)-modified ssDNA as signal probes, one cTnI molecule could induce the release of 4.5 × 104 Pt NPs for collision experiments, greatly enhancing signal conversion efficiency and detection sensitivity. Based on the integration of MBs with RCA, the SPCE immunosensor realized 0.57 fg/mL cTnI detection with a wide linear range of 1 fg/mL to 50 ng/mL. Furthermore, cTnI detection in serum samples of myocardial infarction patients was successfully performed, demonstrating great application prospect of the SPCE immunosensor in clinical diagnosis.

Subnanosecond widely-tunable in the visible spectrum range LBO based optical parametric amplifier

We report realization of a widely-tunable subnanosecond optical parametric amplifier system in LBO crystal pumped by third harmonic of a passively Q-switched Nd:YAG microlaser system. It yields continuous signal wavelength tunability in the visible spectrum range from 460 to 680 nm and idler wavelength — from 740 to 1500 nm. We present experimental data and numerical simulations of our optical parametric amplifier and discuss future improvement directions for greater pump to signal conversion efficiency.

Tunable short-wave near-infrared continuous wave source based on a 532 nm pumped singly resonant optical parametric idler oscillator

We report a continuous wave (CW) singly resonant optical parametric idler oscillator (i-SRO) capable of providing high power, high power conversion efficiency, widely tunable radiation in the short-wave near-infrared (NIR) range. The i-SRO is pumped by a fiber-laser-based laser at 532 nm with a multi-grating, MgO doped periodically poled stoichiometric lithium tantalate (MgO:sPPLT) as quasi-phase matching (QPM) crystal. By utilizing eight grating periods, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, and 8.8 µm of the QPM crystal, with grating tuning and temperature tuning, the i-SRO can be continuously tuned across 951–793 nm and the corresponding idler tunable over 1212–1620 nm. A maximum signal power of 4.9 W for a pump power of 9.1 W and a relevant pump to signal conversion efficiency of ∼53.8% are achieved at the signal of 821 nm. At a pump power of 5.4 W, the output power stability of the signal at 837 nm is better than 2.1% rms, within one hour in Gaussian spatial beam profile. The SRO performance in tuning rate has also been investigated.

Limits of broadband fiber optic parametric devices due to stimulated Brillouin scattering

We experimentally find a practical stimulated Brillouin scattering (SBS) threshold for broadband high-performance fiber optical parametric devices relying on dispersion-stable GeO2-doped silica highly nonlinear fibers. We demonstrate that SBS limits the nonlinear phase shift in such fibers to ~0.3 rad per pump unless the SBS is mitigated in some way. We consequently derive corresponding limits on signal gain and conversion efficiency and find the required SBS mitigation factor for a range of fiber optic parametric devices’ applications. Finally, we examine the level of SBS mitigation using air gaps and fiber tapers for implementation in polarization-insensitive fiber optic parametric devices employing bidirectional loops. We observe that an air gap or fiber taper are not very efficient for SBS mitigation as they provided an increase in SBS threshold up to 0.7 dB attributed primarily to their excess loss.

Octave-spanning mid-infrared femtosecond OPA in a ZnGeP2 pumped by a 2.4 μm Cr:ZnSe chirped-pulse amplifier.

We report on the highly efficient, octave-spanning mid-infrared (mid-IR) optical parametric amplification (OPA) in a ZnGeP2 (ZGP) crystal, pumped by a 1 kHz, 2.4 μm, 250 fs Cr:ZnSe chirped-pulse amplifier. The full spectral coverage of 3-10 μm with the amplified signal and idler beams is demonstrated. The signal beam in the range of ∼3 - 5 μm is produced by either white light generation (WLG) in YAG or optical parametric generation (OPG) in ZGP using the common 2.4 μm pump laser. We demonstrate the pump to signal and idler combined conversion efficiency of 23% and the pulse energy of up to 130 μJ with ∼2 μJ OPG seeding, while we obtain the efficiency of 10% and the pulse energy of 55 μJ with ∼0.2 μJ WLG seeding. The OPA output energy is limited by the available pump pulse energy (0.55 mJ at ZGP crystal) and therefore further energy scaling is feasible with multi-stage OPA and higher pump pulse energy. The autocorrelation measurements based on random quasi-phase matching show that the signal pulse durations are ∼318 fs and ∼330 fs with WLG and OPG seeding, respectively. In addition, we show the spectrally filtered 30 μJ OPA output at 4.15 μm suitable for seeding a Fe:ZnSe amplifier. Our ultrabroadband femtosecond mid-IR source is attractive for various applications, such as strong-field interactions, dielectric laser electron acceleration, molecular spectroscopy, and medical surgery.

Comparison of the Efficiency of Promising Heterostructure Frequency-Multiplier Diodes of the THz-Frequency Range

The results of theoretical and experimental comparison of the signal-conversion efficiency by diodes based on superlattices with a small number of periods (N-like current–voltage characteristic) and promising frequency-multiplier diodes (varactors) (parabolic capacitance–voltage characteristic) are presented.

Dual-periodically poled lithium niobate microcavities supporting multiple coupled parametric processes.

Periodically poled lithium niobate (PPLN) microcavities with additional reciprocal vectors attract attention as a platform for efficient parametric nonlinear optical processes with wavelength and polarization flexibility. Here, we report the simultaneous realization of multiple coupled parametric processes in PPLN microdisk cavities with dual periods as a result of the significantly increased number of reciprocal vectors to fulfill quasi-phase matchings for a series of nonlinear processes. PPLN microdisks with up to 1.43×105 quality factors and unit domain size of 90 nm in width were fabricated using CMOS compatible microfabrication techniques and electrically poled with the help of piezoresponse force microscopy. The conversion efficiency of second-harmonic signal was measured to be 51%W-1. Our work paves the way towards efficient cascaded parametric effects including third- and fourth-harmonic generations.

Variable spin-charge conversion across metal-insulator transition

The charge-to-spin conversion efficiency is a crucial parameter in determining the performance of many useful spintronic materials. Usually, this conversion efficiency is predetermined by the intrinsic nature of solid-state materials, which cannot be easily modified without invoking chemical or structural changes in the underlying system. Here we report on successful modulation of charge-spin conversion efficiency via the metal-insulator transition in a quintessential strongly correlated electron compound vanadium dioxide (VO2). By employing ferromagnetic resonance driven spin pumping and the inverse spin Hall effect measurement, we find a dramatic change in the spin pumping signal (decrease by > 80%) and charge-spin conversion efficiency (increase by five times) upon insulator to metal transition. The abrupt change in the structural and electrical properties of this material therefore provides useful insights on the spin related physics in a strongly correlated material undergoing a phase transition.

Numerical study on mid-infrared optical parametric amplification around 5 µm by injecting signal vector beams in As2Se3 MOFs

The influence of the core diameter and pump wavelength on the phase-matching conditions when different signal vector beams are injected is analyzed numerically in a suspended-core ${{\rm As}_2}{{\rm Se}_3}$As2Se3 microstructured optical fiber (MOF). The idler wavelengths satisfying the phase-matching conditions with different signal vector beams can reach wavelengths of 4.8–5.9 µm in the ${{\rm As}_2}{{\rm Se}_3}$As2Se3 MOFs with different core diameters. By changing the signal vector mode field and adjusting the corresponding signal wavelength, the idler wavelength can be tuned in 754.8 nm from 4.9182 to 5.6730 µm with the pump wavelength changing from 2.80 to 2.90 µm. The influence on signal gain and the idler conversion efficiency is calculated in the ${{\rm As}_2}{{\rm Se}_3}$As2Se3 MOFs with different lengths when injecting different signal vector beams. The peak gain of signal and idler conversion efficiency can reach $\sim{28}\,\, {\rm dB}$∼28dB and $\sim{24}\% $∼24%, respectively, when the different signal vector beams are injected. The simulated results demonstrate that the optical parametric oscillation with wavelengths longer than 5 µm can be realized in chalcogenide fibers with signal vector beam injection.

Gradient magnet design for simultaneous detection of electrons and positrons in the intermediate MeV range.

We report the design and development of a compact electron and positron spectrometer based on tapered neodymium iron boron magnets to characterize the pairs generated in laser-matter experiments. The tapered design forms a gradient magnetic field component allowing energy dependent focusing of the dispersed charged particles along a chosen detector plane. The mirror symmetric design allows for simultaneous detection of pairs with energies from 2 MeV to 500 MeV with an accuracy of ≤10% in the wide energy range from 5 to 110 MeV for a parallel beam incident on a circular aperture of 20 mm. The energy resolution drops to ≤20% for 4-90 MeV range for a divergent beam originating from a point source at 20 cm away (i.e., a solid angle of ∼8 milli steradians), with ≤10% accuracy still maintained in the narrower energy range from 10 to 55 MeV. It offers higher solid angle acceptance, even for the divergent beam, compared to the conventional pinhole aperture-based spectrometers. The proposed gradient magnet is suitable for the detection of low flux and/or monoenergetic type electron/positron beams with finite transverse sizes and offers unparalleled advantages for gamma-ray spectroscopy in the intermediate MeV range.

AlGaN/GaN high-electron-mobility transistor pH sensor with extended gate platform

In this paper, we fabricated an AlGaN/GaN high electron mobility transistor (HEMT) pH sensor with an extended-gate (EG). As the carrier mobility of the transducer that is used as the biosensor is increased, the electrical signal conversion efficiency of the biomaterials is improved. Therefore, the HEMT is a more suitable transducer platform than the conventional silicon-based transistor. The fabricated AlGaN/GaN device showed an electron density of 9.0 × 1012 cm-2, and an electron mobility of 1,990 cm2/V-s. In order to reduce the gate leakage current, which is a drawback of conventional HEMT devices, we deposited a 3-nm thick Al2O3 layer as a top-gate oxide by the atomic layer deposition (ALD) method; the fabricated HEMT has a metal–insulator semiconductor (MIS) structure. In addition, we used the EG to implement the disposable biosensor. Although the EG (a sensing membrane) is contaminated and destroyed, the HEMT (a transducer) can be reused. We evaluated the pH sensing characteristics using a pH sensor, which was implemented by connecting the HEMT and EG. The EG HEMT pH sensor showed a sensitivity of 57.6 mV/pH, which is close to the Nernst limit (approximately 59 mV/pH), and a linearity of 98.93%. To verify the stability and reliability of the implemented EG HEMT pH sensor, we measured the real-time response. The EG HEMT pH sensor has an error of only 2.39% of the signal. Therefore, we expect that the EG-based AlGaN/GaN HEMT pH sensor will be a suitable next-generation biosensor platform for a high electrical signal change efficiency of biomaterials, disposable, and point-of-care systems.

Silicon trench photodiodes on a wafer for efficient X-ray-to-current signal conversion using side-X-ray-irradiation mode

In this paper, we report a direct-conversion-type X-ray sensor composed of trench-structured silicon photodiodes, which achieves a high X-ray-to-current conversion efficiency under side X-ray irradiation. The silicon X-ray sensor with a length of 22.6 mm and a trench depth of 300 µm was fabricated using a single-poly single-metal 0.35 µm process. X-rays with a tube voltage of 80 kV were irradiated along the trench photodiode from the side of the test chip. The theoretical limit of X-ray-to-current conversion efficiency of 83.8% was achieved at a low reverse bias voltage of 25 V. The X-ray-to-electrical signal conversion efficiency of conventional indirect-conversion-type X-ray sensors is about 10%. Therefore, the developed sensor has a conversion efficiency that is about eight times higher than that of conventional sensors. It is expected that the developed X-ray sensor will be able to markedly lower the radiation dose required for X-ray diagnoses.